1. Field of the Invention
The present invention relates to a power supply apparatus configured to supply a power supply voltage or a power supply current to a device under test.
2. Description of the Related Art
A test apparatus includes a power supply apparatus configured to supply a power supply voltage or a power supply current (which will be referred to as the “power supply voltage Vdd” hereafter) to a device under test (DUT). FIG. 1 is a block diagram which shows a schematic configuration of a conventional power supply apparatus. A power supply apparatus 1100 includes a power supply output unit 1026 and a frequency controller (which will be referred to as the “controller” hereafter) 1024 configured to control the power supply output unit 1026. For example, the power supply output unit 1026 is configured as an operational amplifier (buffer), a DC/DC converter, a linear regulator, or a constant current source, and is configured to generate a power supply voltage or a power supply current (output signal OUT) to be supplied to the DUT 1.
A decoupling capacitor C1 is arranged in the vicinity of the power supply terminal of the DUT 1. Furthermore, the output terminal of the power supply apparatus 1100 and the power supply terminal of the DUT 1 are connected via a cable. The target to be controlled by the power supply apparatus 1100 is not the output signal OUT of the power supply output unit 1026, but is the power supply voltage Vdd actually applied to the power supply terminal of the DUT 1. With conventional techniques, the controller 1024 outputs a control value such that the difference between the fed-back observed value (control target) and a predetermined reference value (standard value) becomes zero. Examples of such observed values include a feedback signal that corresponds to the power supply voltage or the power supply current supplied to the DUT 1. For example, a circuit component 1022 represented by a subtractor symbol in FIG. 1 is configured as an error amplifier (operational amplifier), and is configured to amplify the difference between the observed value and the reference value. The controller 1024 configured as an analog circuit generates a control value such that the difference becomes zero. The state of the power supply output unit 1026 is feedback-controlled according to the control value. As a result, the power supply voltage Vdd to be controlled is stabilized to the target value. The parameters to be taken into account in the control operation for a control target 1010 are collectively represented by a symbolic parameter, i.e., a parasitic parameter 1030. The parasitic parameter 1030 includes parasitic resistances, parasitic capacitances, parasitic inductances, and so on, of the power supply cable and internal components of the power supply apparatus 1100.
With conventional techniques, the controller 1024 is configured using an analog circuit. This leads to a problem in that the overall performance of the controller 1024 is fixedly determined by the analog elements that form the controller 1024. Furthermore, the control target 1010 is subject to the effects of fluctuation in the load current, and to the effects of the decoupling capacitor C1 arranged as a peripheral component. In addition, in a case in which the controller 1024 is designed giving consideration to the effects of the parasitic parameter 1030, it results in a complicated circuit configuration and an increased number of circuit components. Moreover, the control performance is fixed according to the circuit configuration. This leads to a problem in which such an arrangement cannot allow the control performance to be changed in a real time manner. A method can be conceived in which multiple circuits are prepared beforehand, and the circuit is switched as necessary. However, such an arrangement leads to an increased circuit area and increased costs, which is not realistic. Furthermore, in order to suppress the effects of temperature drift or the like that can occur in analog elements, there is a need to provide high-precision analog elements or a compensation circuit. This also leads to an increased circuit area and increased costs.